`NH_3` has pyramidal structure with `HNH` bond angle of `107^@` it forms complexes with cation which of the following does not form complex with `NH_3` ?

Options

A. `Ag^(oplus)`
B. `Cu^(2+)`
C. `Cd^(2+)`
D. `Pb^(2+)`

Answer

To determine which cation does not form a complex with ammonia (NH₃), we need to analyze the nature of ammonia and the types of elements it can interact with.

### Step-by-Step Solution:

1. **Understanding Ammonia as a Lewis Base**:
- Ammonia (NH₃) has a lone pair of electrons on the nitrogen atom, making it a Lewis base. This means it can donate its lone pair to form coordinate bonds with cations (Lewis acids).

**Hint**: Remember that Lewis bases donate electron pairs to form complexes.

2. **Identifying the Types of Elements**:
- Ammonia typically forms complexes with transition metals, which are found in the d-block of the periodic table. These metals can accept electron pairs from ammonia due to their ability to accommodate additional electrons in their d-orbitals.

**Hint**: Focus on the periodic table and identify which elements are transition metals (d-block).

3. **Analyzing the Given Cations**:
- The question provides several cations. We need to identify which one is not a transition metal:
- **Ag⁺ (Silver)**: A transition metal (d-block).
- **Cu²⁺ (Copper)**: A transition metal (d-block).
- **Cd²⁺ (Cadmium)**: A transition metal (d-block).
- **Pb²⁺ (Lead)**: A p-block element, not a transition metal.

**Hint**: Check the group and block of each element to determine if they are transition metals.

4. **Conclusion**:
- Since lead (Pb²⁺) is a p-block element and does not belong to the d-block, it cannot form complexes with ammonia. Therefore, the cation that does not form a complex with NH₃ is **Pb²⁺**.

**Final Answer**: Lead (Pb²⁺) does not form a complex with NH₃.

### Summary of Steps:
- Identify ammonia as a Lewis base.
- Recognize that ammonia forms complexes with d-block (transition) metals.
- Analyze the cations provided and determine which is not a transition metal.
- Conclude that lead (Pb²⁺) does not form complexes with NH₃.